This invention relates to the field of archery bows of the so-called compound type in which some kind of mechanism is provided to progressively reduce the resistance of the drawstring as it is pulled back to the fully cocked position and conversely to progressively increase the force of the drawstring when released to snap back to the fully released position. Examples of prior art bows of this kind are disclosed in the following U.S. Patents, No. 3,486,495 to Allen dated Dec. 30, 1969; No. 3,744,473 to Nishioka dated July 10, 1973; No. 3,812,835 to Smith dated May 28, 1974; No. 3,851,638 to Alexander dated Dec. 3, 1974; No. 3,854,467 to Hofmeister dated Dec. 17, 1974; No. 3,923,035 to Trotter dated Dec. 2, 1975; No. 3,923,036 to Jennings et al dated Dec. 2, 1975; No. 3,945,368 to Jones dated Mar. 23, 1976; No. 3,958,551 to Ketchum dated May 25, 1976; No. 3,967,609 to Frydenlund dated July 6, 1976 and No. 3,981,290 to Islas dated Sept. 21, 1976.
The prior art compound bows generally utilize an arrangement of pulleys by which to accomplish a reduction of drawstring resistance, and this in turn requires some means to synchronize the rotation of the pulleys which are associated with the upper and lower limbs of the bow. Such synchronization generally took the form of connecting the pulley mechanism which was mounted on one limb to the other limb at some intermediate anchor point by means of a line or cable under tension.
The present invention does not use a pulley mechanism, but employs pivot members which rotate less than a full turn from their position when the drawstring is fully released to their position when the drawstring is fully drawn and the bow cocked. The pivot members act both as a variable leverage mechanism and as a synchronization mechanism. In accordance with this invention, each pivot member applies variable leverage to both limbs. The result is an improved compound bow over those in the prior art, and one that performs the variable leverage and synchronization functions with a simplified less expensive mechanism.